Limited angle dc torque motor

ABSTRACT

A torque motor has a stator including a ringlike magnetic casing containing four circumferentially spaced radial magnetic poles. The casing is closed by a base and cover. Wire coils connected in series are wound on two poles or on all four poles. Thin magnetic webs connect the poles and define a ring in which rotates a permanent magnet rotor. The magnetic ring constitutes a magnetic bridge which permits the rotor to float freely when the coils are deenergized. A spring or auxiliary magnetic means is provided to return the rotor to a predetermined angular position.

[ Feb. 22, 1972 United States Patent Skrobisch 3,076,111 1/19633,047,750 7/1962 Brown 3,539,846 11/1970 JewelL...

3,152,275 10/1964 Aske.............

3,139,571 6/1964 Tuckeretal....................

Primary Examiner-D. F. Duggan AnomeyEdward H. Loveman [22] Filed: Dec.8, 1970 [21] Appl.No.: 96,134

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constitutes a magnetic bridge which permits the rotor to float freelywhen the coils are deenergized. A spring or auxiliary UNITED STATESPATENTS 1,202,446 10/1916 Speed 3,483,410 12/1969 magnetic means isprovided to return the rotor to a predetermined angular position.

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10 Claims, 12 Drawing Figures 7 PATENTEDFEBZZ I912 SHEET 1 BF 2 INVENTOR.

ALF-RE 0 SKROBISCH ATTORNEY IPATENTEDFEBZIZ I972 sum 12 0F 2 FIG llINVENTOR ALFRED SKROBISCH FIG. I2

' INPUT ATTORNEY LIMITED ANGLE DC TORQUE MOTOR This invention concerns alimited angle DC torque motor and more specifically concerns a limitedangle DC torque motor of the type having a permanently magnetized rotorrotating within a stator having coils energized by an external directcurrent source for turning the rotor.

I-Ieretofore torque motors of miniature size used in a servomechanismfor turning a shaft angularly in a range not exceeding 180 have hadrather limited torque outputs. Such motors generally employ apermanently magnetized two-pole rotor rotatably supported in a stator onwhich is wound a coil or coilsenergized by an external direct currentsource. The small torque output is affected adversely by loss ofmagnetic flux in the airgap between the rotor and the magnetic parts ofthe stator. A further reduction in torque is caused by the strong biasof a return spring which is generally employed to return the rotor to aninitial zero" position, but which opposes turning of the rotor when thestator is energized.

It is particularly important in a torque motor of the type described,that the rotor rotate as freely as possible in the stator since therotor is often called upon to respond to changes in the actuatingmagnetic field of the stator, occuring as frequently as several hundredtimes per second. This condition is encountered when the torque motorsare used in a loop of a servomechanism to drive chart recording pens andpointers of indicators of various kinds.

According to the present invention, the novel torque motor has a statorformed with four magnetic poles spaced 90 apart. Wire coils may be woundon two or four of the poles.-Extending circumferentially around therotor and between poles is a thin ring or bridge which minimizes theairgap between the rotor and the stator and serves as a magnetic bridgeso that the rotor floats freely when the direct current supplied to thecoils is turned off. A return spring may be provided for returning therotor to a zero position. A feedback potentiometer may be mounted nearthe rotor with a wiper arm carried by the rotor. This potentiometer isconnected in a feedback circuit to the input of a DC amplifier supplyingthe current to the coils of the motor. The arrangement described makesit possible to construct a miniature torque motor exerting much greatertorque than has heretofore been attainable with conventional torquemotors of comparable size. Furthermore angular deflections of the .rotorare accomplished with lower applied current.

Accordingly, it is a principal object of the instant invention toprovide an angularly limited DC permanent magnetic torque motor havinglarge torque output.

Another object of the instant invention is to provide such a torquemotor having little loss of magnetic flux in the airgap between therotor and the magnetic parts.

These and other objects and many of the attendant advantages of thisinvention will be readily appreciated as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawing in which:

FIG. 1 is an external perspective view of a torque motor embodying theinvention;

FIG. 2 is an enlarged plan view of the motor with cover removed andinverted;

FIG. 3 is a cross-sectional view taken along line 33 of FIG. 2;

FIG. 4 is an enlarged plan view of the base of the motor;

FIG. 5 is an exploded perspective view of parts of the motor of FIG. 1;

FIG. 6 is a cross-sectional view similar to a portion of FIG. 3, showinganother spring return means for the rotor;

FIG. 7 is a cross-sectional view taken along line 7-7 of FIG. 6;

FIG. 8 is a top plan view showing an embodiment of the torque motor withfour coils;

FIG. 9 is a top plan view showing a further torque motor with a ringinsert magnetically bridging the rotor;

FIG. I0 is an exploded perspective view of the ring insert and polestructure employed in the motor of FIG. 9;

FIG. 11 is a top plan view showing another torque motor with four coilsand a bridging ring insert; and

FIG. 12 is a diagram of a torque motor and an associated power supplyand feedback circuit.

Referring now to the drawings wherein like reference charactersdesignate like or corresponding parts throughout, there is illustratedin FIGS. 1 through 5 a torque motor generally designated as referencenumeral 15 which includes a central cylindrical stator or casing 20, acuplike cover 22 and a cuplike base 24. As best illustrated in FIGS. 3and 5 each end of the casing 20 is formed with a circumferential rabbet26, 28 which engage a mating circumferential lip 30 of the base and asidewall 32 of the cover respectively so that the entire assembly iscylindrical and of uniform external diameter as shown in FIG. I. A pairof aligned holes 31, 33 in the base and the cover respectively receive apair of screws 35 to hold the parts together. The casing 20 is a ringmade of highly permeable magnetic material such as soft iron which hassnugly fitted therein a pole structure 34 having four radial poles 36-39each of which is joined by a thin circumferentially extending integralweb 40 constituting a bridge between the poles (see FIGS. 2, 3, 5). Thepole structure has a central hole 42 bounded by the four webs 40 and theinner ends of the four poles. A pair of generally rectangular wire coils44, 46 are mounted on diametrically opposite poles 36 and 38,respectively and connected together in series. The coils are wound sothat one pole is a NORTH magnetic pole whole the diametrically oppositepoles is a SOUTH pole when the coils are energized. Rotatably mountedinside the casing 20 is a per.- manently magnetized cylindrical rotor 50having a permanently magnetized body 51 with diametrically oppositeNORTH and SOUTH poles. The circumferential air gap 52 is just sufficientto provide rotational clearance for the rotor 50 and may be as small as0.005 of an inch. It'will be noted that the central hole 42 is notobstructed by the coil windings 44, 46 as occurs in prior torque motors.

The thin webs or bridges 40 serve to concentrate magnetic flux to suchan extent that they are normally saturated when the coils are energized.Under this condition, the saturated bridges have a negligible effect indiverting the magnetic field used to produce rotation of the rotor 50.However, when'the coils are deenergized. the bridge structure 40 servesas a magnetic shield or keeper that is no longer saturated whereby the Nand S poles of the permanent magnet rotor 50 are not attracted to anyparticular point around the surrounding bridge structure and thus therotor in effect floats free when the coils are deenergized. Thischaracteristic is very important since it insures instantaneous responseto any change in energization of the coils to deflect the rotor in onedirection or another.

The rotor has a central axial shaft 60 which may carry a pointer 61 atits upper end see FIG. 1. The shaft 60 has a pivot point 63 at its lowerend rests'on a jeweled bearing 62 located in the end of a screw 64inserted in a threaded hole 66 at the bottom 68 of the base 24. Theshaft also carries a small magnetized disk 70 spaced axially from rotorbody 51 by a nonmagnetic spacer 72 (see FIGS. 2 and 3). Mounted on thebase 24 is a pair of small diametrically opposed bar magnets 74 whichtend to turn the rotor to a predetermined zero position with its N polelocated somewhere between the poles 36 and 38 of the stator 20. Thismagnetic return arrangement for the rotor exerts a negligible bias sothat the turning torque applied to rotor 50 by the magnetic fieldcreated by the energized coils is not materially reduced. The screws 35extend through a pair of holes 41 in the poles 37, 39 to hold the polestructure 34 in place in the stator 20.

Mounted on top of the rotor body 51 is a pair of wiper arms 75 spaced bya pair of insulators 76, 77. The arms 75 contact a resistor 78 on theplate 80 mounted inside of the cover 22. The arms and resistorconstitute a potentiometer (FIG. 12) which is varied in resistancebetween a pair of wire leads 82 connected to the wiper arms 75 as therotor turns to different angular positions (FIG. 2). These leads alongwith a pair of leads 84 connected to the coils 44, 46 and a pair ofleads 86 connected to the resistor 78 extend through an opening 88provided in the side of the cover 22. The leads may be connected to anexternal circuit such as a circuit 100 shown in FIG. 12. The shaft 60extends through a hole 89 in the cover 22.

In the circuit 100 shown in FIG. 12, signals are applied to a directcurrent amplifier 102 whose output is connected to coils 44, 46 of themotor 15. The shaft 60 drives arms 75 of the potentiometer 120 whoseresistor 78 is connected in circuit with the arms 75 to the input of theamplifier 102 in a conventional feedback circuit. A feedback signalwhich is proportional to the angular deflection of the shaft 60 is thusapplied to the amplifier input.

In FIGS. 6 and 7 is shown part of another torque motor 15A in whichparts corresponding to those of motor 15 are identically numbered. Inthis motor, the inner end of a coil spring 125 is attached to anonmagnetic disk 128 secured to the shaft 60 and the body 51. The outerend of the spring 125 is secured to the inside wall of the base 24a.This spring serves to return the angularly turned rotor to apredetermined zero or initial position when current is cut off from thecoils 44, 46.

FIG. 8 shows another torque motor 158 which is basically the same astorque motor 15 except that four coils 36a, 37a, 38a and 390 areconnected in series and mounted on the four poles 36-39 respectively ofthe pole structure. Other parts correspondingto those of torque motor 15are identically numbered. The body 510 of rotor 50a is permanentlymagnetized in quadrature with four alternating N and S poles spacedangularly 90". apart. The torque motor 15B will have a smaller angularrange than that of motor 15, i.e., somewhat less than 90 but thisangular extent will suffice for many indicating, metering and recordingapplications. More significantly a torque motor with this configurationwill produce a torque several times greater than that produced by thetorque motor of FIGS. 1-5.

FIGS. 9 and 10 show an alternate pole and magnetic bridge structure fortorque motor C. Here poles 36b-39b are integral with the ringlike case aand extend radially outward therefrom with the coils 44 and 46 mountedon diametrically opposite poles. A thin ring 150 made of a magneticmetal is snugly fitted inside the poles and defines a magnetic bridgestructure equivalent to the webs 40 of motor 15.

FIG. 1 1 shows a torque motor 15D employing the same ring 150 and case20a as motor 15C, but has four coils 36a-39a mounted on the four poles36b-39b respectively. This motor operates like motor 158 with hightorque but with an angular range of the quadrature magnetized rotor 50alimited to less than 90".

All of the torque motors ISB-ISD may employ spring return or magneticreturn means for the rotor as shown in FIGS. 4 and 7.

It should be understood that the foregoing relates to only preferredembodiments of the invention, and that it is intended to cover allchanges and modification of the example of the invention herein chosenfor the purposes of the disclosure, which do not constitute departuresfrom the spirit and scope of the invention.

The invention claimed is:

i l. A limited angle DC torque motor adapted to be energized by a directcurrent, comprising a stator including a generally cylindrical ringlikecasing with four fixed magnetizable poles extending radially in sidesaid casing and spaced circumferentially apart, said stator including atin magnetic bridging means magnetically connecting the inner ends ofsaid poles and defining a ,central hole in said casing,

a pair of serially wound wire coils wound respectively on of saidcentral hole, a shaft extending axially of said 'rotor and rotatabletherewith and, a base means connected to said casing at one end thereoffor rotably supporting said rotor with respect to said stator therebypermitting angular rotation therein when said coils are energized bysaid direct current, whereby said rotor will float freely within saidstator when said coils are deenergized due to said magnetic bridgingmeans.

2. A limited angle DC torque motor as defined in claim 1 wherein saidbase means includes bias means for angularly turning said rotor to apredetermined position when said coils are deenergized. v

3. A limited angle DC torque motor as defined in claim 2 furthercomprising a cover at the other end of said casing,

a first potentiometer means supported by said cover, and,

a second potentiometer means carried by said rotor and arranged forcooperation with said first potentiometer means when said first andsecond potentiometer means are energized by said direct current.

4. A limited angle DC torque motor as defined in claim 1, wherein saidmagnetic bridging means is a ringlike structure including thin magneticmetal webs integral with said poles.

5. A limited angle DC torque motor as defined in claim I wherein saidmagnetic bridging means is a tin ring snugly fitted inside of said polesand said poles being integrally formed with said casing.

6. A limited angle DC torque motor adapted to be energized by a directcurrent, comprising a stator including a generally cylindrical ringlikecasing with four fixed magnetizable poles extending radially in sidesaid casing and spaced circumfere ntially apart, said stator including athin magnetic bridging means magnetically connecting the inner ends of-said.poles and defining a central hole in said casing,

a wire wound coil wound on each of said poles said coils being woundserially such that adjacent poles have opposite polarities when thecoils are energized by said direct current,

a permanently magnetized four-pole rotor extending axially of saidcentral hole,

a shaft extending axially of said rotor and rotable therewith,

and

a base means connected to said casing at one end thereof for rotablysupporting said rotor with respect to said stator thereby permittingangular rotation therein when said coils are energized by said directcurrent, whereby said rotor will float freely within said stator whensaid coils are deenergized due to said magnetic bridging means.

7. A limited angle DC torque motor as defined in claim 6 wherein saidbase means includes bias means for angularly turning said rotor to apredetermined position when said coils are deenergized.

8. A limited angle DC torque motor as defined in claim 7 furthercomprising a cover at the other end of said casing, I

a first potentiometer means supported by said cover, and,

a second potentiometer means carried by said rotor and arranged forcooperation with said first potentiometer means when said first andsecond potentiometer means are energized by said direct current.

9. A limited angle DC torque motor as defined in claim 6, wherein saidmagnetic bridging means is a ringlike structure including thin magneticmetal webs integral with said poles.

10. A limited angle DC torque motor as defined in claim 6 wherein saidmagnetic bridging means is a thin ring snugly fitted inside of saidpoles and said poles being integrally formed with said casing.

1. A limited angle DC torque motor adapted to be energized by a directcurrent, comprising a stator including a generally cylindrical ringlikecasing with four fixed magnetizable poles extending radially in sidesaid casing and spaced circumferentially apart, said stator including atin magnetic bridging means magnetically connecting the inner ends ofsaid poles and defining a central hole in said casing, a pair ofserially wound wire coils wound respectively on two diametricallyopposed poles, a permanently magnetized two pole rotor extending axiallyof said central hole, a shaft extending axially of said rotor androtatable therewith and, a base means connected to said casing at oneend thereof for rotably supporting said rotor with respect to saidstator thereby permitting angular rotation therein when said coils areenergized by said direct current, whereby said rotor will float freelywithin said stator when said coils are deenergized due to said magneticbridging means.
 2. A limited angle DC torque motor as defined in claim 1wherein said base means includes bias means for angularly turning saidrotor to a predetermined position when said coils are deenergized.
 3. Alimited angle DC torque motor as defined in claim 2 further comprising acover at the other end of said casing, a first potentiometer meanssupported by said cover, and, a second potentiometer means carried bysaid rotor and arranged for cooperation with said first potentiometermeans when said first and second potentiometer means are energized bysaid direct current.
 4. A limited angle DC torque motor as defined inclaim 1, wherein said magnetic bridging means is a ringlike structureincluding thin magnetic metal webs integral with said poles.
 5. Alimited angle DC torque motor as defined in claim 1 wherein saidmagnetic bridging means is a tin ring snugly fitted inside of said polesand said poles being integrally formed with said casing.
 6. A limitedangle DC torque motor adapted to be energized by a direct current,comprising a stator including a generally cylindrical ringlike casingwith four fixed magnetizable poles extending radially in side saidcasing and spaced circumferentially apart, said stator including a thinmagnetic bridging means magnetically connecting the inner ends of saidpoles and defining a central hole in said casing, a wire wound coilwound on each of said poles said coils being wound serially such thatadjacent poles have opposite polarities when the coils are energized bysaid direct current, a permanently magnetized four-pole rotor extendingaxially of said central hole, a shaft extending axially of said rotorand rotable therewith, and a base means connected to said casing at oneend thereof for rotably supporting said rotor with respect to saidstator thereby permitting angular rOtation therein when said coils areenergized by said direct current, whereby said rotor will float freelywithin said stator when said coils are deenergized due to said magneticbridging means.
 7. A limited angle DC torque motor as defined in claim 6wherein said base means includes bias means for angularly turning saidrotor to a predetermined position when said coils are deenergized.
 8. Alimited angle DC torque motor as defined in claim 7 further comprising acover at the other end of said casing, a first potentiometer meanssupported by said cover, and, a second potentiometer means carried bysaid rotor and arranged for cooperation with said first potentiometermeans when said first and second potentiometer means are energized bysaid direct current.
 9. A limited angle DC torque motor as defined inclaim 6, wherein said magnetic bridging means is a ringlike structureincluding thin magnetic metal webs integral with said poles.
 10. Alimited angle DC torque motor as defined in claim 6 wherein saidmagnetic bridging means is a thin ring snugly fitted inside of saidpoles and said poles being integrally formed with said casing.